Method for the environmentally sound disposal of air/solvent mixtures using a fuel cell system and recovery unit

ABSTRACT

The invention relates to a method for the environmentally sound disposal of air/solvent mixtures which are made of combustible gaseous vaporous or liquid waste products, using a fuel cell system for the recycling of the air/solvent mixtures while removing the environmentally compatible exhaust air developing in the fuel cell system, the waste heat that is produced and the electric power that is produced.

The invention relates to a method for the environmentally sound disposal of air/solvent mixtures which consist of combustible gaseous, vaporous or liquid waste materials, with a fuel-cell plant for the utilization of the air/solvent mixtures, along with the discharge of the environmentally compatible exhaust air occurring in the fuel-cell plant and of the generated waste heat and of the generated electrical current.

According to the prior art (see FIGS. 1 and 2), for example, air/solvent mixtures have to be delivered for thermal postcombustion (TPC), so as not to cause any harmful substances to enter the environment. For reasons of prescribed safety, for example, air/solvent mixtures, such as leave the user process, must be diluted with air to an extent such that no ignitable mixture occurs. This depleted air is delivered for thermal postcombustion. Sometimes, for this purpose, the mixture air is preheated by means of the waste heat from the subsequent combustion process, before it reaches the combustion chamber for thermal postcombustion.

The air/solvent mixture, preheated or not, enters the combustion chamber, and this is usually fired with fuel, for example fuel gas or electric energy. Catalytic postcombustions may also be envisaged.

If a fuel cell (FC) is used instead of thermal postcombustion, the air/solvent mixture can also be burnt, for example, in order to maintain the operating temperature. The electrical current is generated via a separate circuit of fuel gas or combustible materials.

The concepts according to the prior art require fuel gas in order to burn combustible materials.

The object underlying the invention is to improve a method for the environmentally sound disposal of air/solvent mixtures according to the preamble of claim 1.

According to the invention, this object is achieved in that the air/solvent mixtures are delivered partially or completely to a recovery unit and are converted there into a usable energy form, and these are delivered partially or completely to the fuel-cell plant for utilization, and consequently, during operation, the fuel-cell plant is automatically supplied partially or completely with fuel, and the fuel-cell plant operates on the basis of a molten carbonate fuel cell. Such a fuel-cell plant is also designated as a molten carbonate fuel cell or plant.

Air/solvent mixtures are understood to mean air and/or inert gas and/or mixtures thereof with combustible or burnable materials (also designated below as a mixture). Solvents are, for example, alcohols, ketones, such as acetone, aromatics, such as toluene. Such solvents are also designated as VOC (volatile organic compounds).

Fuel-cell plants based on a molten carbonate fuel cell are known, for example, from DE 195 48 297 02 and have the advantage that, by means of these, energy carriers can be supplied with current with high electrical efficiency.

Particular features according to the invention of the fuel-cell plant based on a molten carbonate fuel cell is the arrangement in which all the hot plant components are accommodated in a housing and in which the fuel-cell stack is supported in a horizontal position, with the fuel entry side downward, on a gas inlet hood and is at the same time sealed off automatically by means of its own weight.

In an inventive refinement, the air/solvent mixtures in the recovery unit are condensed out in a condensation device, and the burnable condensate obtained after treatment in a gas treatment plant, is converted electrochemically into fuel gas in the anode space of the fuel-cell plant.

The exhaust air which emerges from the recovery unit and has been largely freed of air/solvent mixtures is delivered preferably as fresh air to the cathode spaces of the fuel-cell plant, and the solvent constituents contained are oxidized by oxygen.

According to the invention, the waste heat generated in the fuel-cell plant and/or the current are/is delivered to the recovery unit for condensing out the air/solvent mixture.

The method or plant concept, according to the invention, during operation, utilizes largely or solely the energy which is contained in the combustible material which has previously been condensed out from the air/solvent mixture. Only the start-up may optionally take place by means of a conventional fuel, such as fuel gas.

In a further refinement of the invention, the recovery unit is an absorption plant, condensation plant, inversion cold plant or adsorption plant.

In a development of the invention, the burnable or combustible materials are removed completely or virtually completely from the mixture or the air/solvent mixture, and the residual gas fraction from the mixture is delivered to the supply air of the fuel-cell plant.

FIG. 1 shows the prior art, that is to say, diagrammatically, a method for the environmentally sound disposal of air/solvent mixtures 5 which consist of combustible vaporous or liquid waste materials, by means of a combustion unit 1, along with the discharge of the environmentally compatible exhaust air 2 occurring in the combustion unit 1 and of the generated waste heat 3 and/or current 4.

The combustion unit 1 here is a thermal postcombustion plant 9 into which an air/solvent mixture 5 is introduced. The air/solvent mixture 5 has been diluted with air to an extent such that there is no ignitable mixture present. This depleted air is delivered for thermal postcombustion. For combustion, a fuel/fuel gas 11 and/or electric energy 12, that is to say current, are/is introduced into the postcombustion plant 9. The exhaust air 2 (CO₂/H₂O) and the waste heat 3 are discharged from the postcombustion plant 9. It is also known to use the waste heat 3 for preheating the air/solvent mixture 1.

FIG. 2 likewise shows the prior art, for example U.S. Pat. No. 6,845,619 B2, except that, here, the combustion unit 1 used is a fuel-cell plant 10 for which a solvent 5 is employed as fuel gas. The exhaust air 2, the waste heat 3 and current 4 are discharged from the fuel-cell plant 10.

FIG. 3 describes the novel coupling of a fuel-cell plant 10 and a recovery unit 6, the fuel-cell plant 10 carrying out a conversion of the air/solvent mixture 5 into heat energy and exhaust air or exhaust gas or current. The fuel-cell plant 10 supplies the recovery unit 6 with waste heat which has been obtained from the combustible or burnable material.

Part of the air/solvent mixture 5 can be introduced directly into the cathode spaces of the fuel cells of the fuel-cell plant, and another part of the remainder is introduced into the recovery unit 6 for condensation, and is converted there into usable energy forms, and these are then introduced, after conversion in hydrogen in a reformer, into the anode spaces of the fuel cells of the fuel-cell plant as fuel gas. In the anode spaces, the hydrogen is reacted electrochemically according to the following reaction equation:

H₂+CO₃ ²⁻→H₂O+CO₂+2e⁻

The recovery unit 6 separates the air/solvent mixture 5. The combustible or burnable material (the condensate 7) is transferred into a tank 8, and from this, in turn, the fuel-cell plant 1 can extract the fuel necessary for operation.

The air/solvent mixture 5 is thus introduced into the recovery unit 6 and is condensed out there. The condensate 7 is conducted into a tank 8. In addition to the air/solvent mixture 5, exhaust air 2 and/or waste heat 3 or current occurring in the combustion unit are/is introduced into the recovery unit 6. This exhaust air and/or waste heat, if appropriate also supplemented by electric energy 12, are/is used for material conversion or for condensation. The exhaust air 17 arousing in the recovery unit 6 is, for example, discharged from the recovery unit 6 and introduced into the cathode spaces of the fuel cells of the fuel-cell plant. The solvent still contained in the exhaust air is burnt as a result of oxidation by oxygen in the hot surroundings of the cathode space to form CO₂ and H₂O. In so far as solvent constituents still not oxidized leave the cathode space, these are converted into harmless constituents in the following catalytic burner by combustion. The set-up of a corresponding fuel-cell plant is illustrated, for example, in DE 195 48 297 C2.

The condensate 7 is stored in the tank 8 until it is used as liquid burnable material 15 in the fuel-cell plant 1 or is delivered for another use 14. A more extensive material conversion 16 may also be carried out optionally in a corresponding converter, in which case electric energy or process heat can be delivered for material conversion 16.

The fuel-cell plant 1 is a fuel-cell plant of the molten carbonate type. Fuel/fuel gas 11 coming from another source may, if required, also be introduced into the fuel-cell plant 1. The exhaust air 2 and waste heat 3 from the combustion process are transferred at least partially into the recovery unit 6 where they are used for the condensation of the air/solvent mixture 5. The exhaust gas 18 (CO₂/H₂O) is discharged.

Features of the method according to the invention, also called a plant concept below, are described below.

-   -   1. The plant concept serves for the environmentally sound         disposal of mixtures of air and of combustible or burnable         materials and avoids the use of additional fuel gas for the         combustion of burnable or combustible materials.     -   2. The plant concept is characterized in that a coupling of         fuel-cell plant and recovery unit is carried out. The fuel-cell         plant is a fuel-cell plant based on a molten carbonate fuel         cell. Recovery units may be, for example, absorption plants,         condensation plants, inversion cold plants, adsorption plants.     -   3. The fuel-cell plant does not rely on the constant         concentration of combustible materials in the air mixture, but         could be operated uniformly by means of the continuous         extraction of combustible materials from the tank.     -   4. As a result of the continuous extraction of combustible         materials from the tank, the plant can even be operated should         the supply of air/solvent mixture or condensate or of burnable         liquid material be interrupted.     -   5. By the use of a fuel-cell plant, electrical current is also         obtained from the combustible material in addition to the waste         heat.     -   6. The combustible material from the tank does not have to be         utilized completely via the plant concept, but may optionally be         partially delivered for other applications.     -   7. The essential property of the coupling of the fuel-cell plant         to the recovery unit is the conversion of waste heat into         exhaust air or exhaust gas. By the use of a fuel-cell plant,         electrical current is also incorporated into the coupling. 

1-5. (canceled)
 6. A method for the environmentally sound disposal of air/solvent mixtures which comprises combustible gaseous, vaporous or liquid waste materials, with a fuel-cell plant for the utilization of the air/solvent mixtures, along with the discharge of the environmentally compatible exhaust air occurring in the fuel-cell plant and of the generated waste heat and of the generated electrical current, comprising delivering the air/solvent mixtures partially or completely to a recovery unit and converting the air/solvent mixture into a usable energy form, and partially or completely delivering the usable energy form to the fuel-cell plant for utilization, and consequently, during operation, the fuel-cell plant is automatically supplied partially or completely with fuel, and the fuel-cell plant operates on the basis of a molten carbonate fuel cell.
 7. A method as claimed in claim 7, wherein the air/solvent mixture in the recovery unit is condensed out in a condensation device, and the burnable condensate obtained, after treatment in a gas treatment plant, is converted electrochemically into fuel gas in the anode spaces of the fuel-cell plant.
 8. A method as claimed in claim 6, wherein the exhaust air which emerges from the recovery unit and has been largely freed of air/solvent mixtures is delivered as fresh air to the cathode spaces of the fuel-cell plant, and the solvent constituents contained are oxidized by oxygen.
 9. A method as claimed in claim 7, wherein the exhaust air which emerges from the recovery unit and has been largely freed of air/solvent mixtures is delivered as fresh air to the cathode spaces of the fuel-cell plant, and the solvent constituents contained are oxidized by oxygen.
 10. A method as claimed in claim 6, wherein the waste heat generated in the fuel-cell plant or the current is delivered to the recovery unit for condensing out the air/solvent mixture.
 11. A method as claimed in claim 7, wherein the waste heat generated in the fuel-cell plant or the current is delivered to the recovery unit for condensing out the air/solvent mixture.
 12. A method as claimed in claim 8, wherein the waste heat generated in the fuel-cell plant or the current is delivered to the recovery unit for condensing out the air/solvent mixture.
 13. A method as claimed in claim 9, wherein the waste heat generated in the fuel-cell plant or the current is delivered to the recovery unit for condensing out the air/solvent mixture.
 14. A method as claimed in claim 6, wherein the recovery unit is an absorption plant, condensation plant, inversion cold plant or adsorption plant.
 15. A method as claimed in claim 7, wherein the recovery unit is an absorption plant, condensation plant, inversion cold plant or adsorption plant.
 16. A method as claimed in claim 8, wherein the recovery unit is an absorption plant, condensation plant, inversion cold plant or adsorption plant.
 17. A method as claimed in claim 9, wherein the recovery unit is an absorption plant, condensation plant, inversion cold plant or adsorption plant.
 18. A method as claimed in claim 10, wherein the recovery unit is an absorption plant, condensation plant, inversion cold plant or adsorption plant.
 19. A method as claimed in claim 11, wherein the recovery unit is an absorption plant, condensation plant, inversion cold plant or adsorption plant.
 20. A method as claimed in claim 12, wherein the recovery unit is an absorption plant, condensation plant, inversion cold plant or adsorption plant.
 21. A method as claimed in claim 13, wherein the recovery unit is an absorption plant, condensation plant, inversion cold plant or adsorption plant. 